1. Field of the Invention
The present invention relates to a method for the manufacture of stacked type or wound type capacitors, and more especially to a method for the manufacture of capacitors using metallized polyethylene naphthalene films.
At present, to make stacked or wound type capacitors, the general practice is to use a plastic film such as a metallized polyester, polypropylene, polysulfone or polycarbonate film in the form of disk-shaped slabs. The disk-shaped slabs generally come from a roll of plastic film of great width which has been metallized and cut out so as to form disk-shaped slabs having a metallized zone and non-metallized lateral margin. To make a capacitor, at least two films of the above type are superimposed, their respective metallized non-lateral margins being positioned on opposite sides so as to obtain a pair of films constituted by an even-order film and an odd-order film. To obtain a stacked type of capacitor, at least one pair of films is wound in a known way about a large-diameter wheel in a determined number of turns so as to obtain a capacitive strip that has alternating even-order and odd-order layers. To obtain a wound type of capacitor, at least one pair of films is wound about a spindle or similar device. Then, in both cases, each of the lateral faces of either the capacitive strip or the wound capacitor is covered with an electrically conductive material in order to make the electrical connections. The covering is done by the metallization of the same-order layers during an operation known as schoopage or Schoop's metal spray process.
For many years, it has been sought to improve the stability of the characteristics, notably the stability in temperature, by using types of metallized plastic films other than the plastic films mentioned above. Now, in the past few years, metallized polyethylene naphthalene films have come into the market. Polyethylene naphthalene has a number of advantages, notably with respect to its melting point and its glass-transition temperature. However, it has been observed that the capacitors obtained by using this material as it is in the manufacture of stacked or wound type capacitors cannot be used in applications such as surface-mounting by reflow soldering or by vapor phase deposition, or in any applications calling for resistance to high temperature.